Edit UI, Create UI: fix slow builds

[severinbeauvais]

Since some semi-unrelated PRs were linked to this ticket, I update this ticket's ticket, description, etc accordingly, and moved the previous content to #16500.

Travis and I realized that the builds had gotten slow, and sometimes hung, as a result of a recent PR. This ticket is to keep track of that work and time.

• investigate what impacted the build - I found that a vue package update caused this
• fix Edit UI accordingly
• fix Create UI accordingly

[severinbeauvais]

I deleted some obsolete comments from above and updated #16500 accordingly.

[severinbeauvais]

Test Notes

There is nothing in particular to test for this. Verifying that the build and unit tests succeed should prove that the code works after these changes.

Note that we were using the current version of vue (2.7.10) for several months without issue, so I think it should still be OK.